Tall, slender and very English, Francis Crick, who has died of colon cancer aged 88, was one of that rare group of scientists whose work changed man's perception of himself and of the natural world.

With James Watson, at Cambridge, and Maurice Wilkins, at King's College London, who was also using the work of Rosalind Franklin, Crick unmasked the so-called "blueprint of life" - the extraordinarily accurate process of biological replication and the elegant helical biochemistry on which the stuff of genes depends. In many ways, their contribution to biology was as great as that a century earlier, when Darwin presented a logical unification of evolution.

But while Darwin's ideas were met as much with hostility as acclaim, those of Crick, Watson and Wilkins, who shared the 1962 Nobel prize for physiology and medicine for their work, fell, scientifically speaking, on prepared minds. A few days after the publication of the famous first paper on the structure of DNA, the entire biochemistry department at Oxford journeyed to Cambridge to question, and then admire, the Watson-Crick model of the double helix and its cross-linking. The Oxford group sent a telegram: "Congratulations - sender Gene". Some still think it should have read: "Be careful - sender God".

However this may be, Crick, a wartime physicist turned biologist, holds an equal niche in the history of biology with Watson, an American biologist at Cambridge, for the joint creation of the Watson-Crick hypothesis which unmasked the central mystery of genetics, and revealed both the structure of DNA and its elegant code. Wilkins' role lay primarily in the meticulous preparation and interpretation of X-ray diffraction information, giving precise dimensions for the double helical structure.

It was Crick who, in the famous paper of April 25 1953, offered one of the great understatements of literature, scientific or otherwise: "It has not escaped our notice that the specific pairing [of purine and pyrimidine bases] that we have postulated immediately suggests a possible copying mechanism for the genetic material." They were the first to reach this fiercely sought biological Holy Grail.

Five weeks later, their claim was put beyond doubt by a second paper, in which Crick explained in detail how genes need to employ only sequences of the main bases in matched pairs to specify, by positive and negative imprint, the precise and unique amino acid sequence of any protein, whatever its complexity. When Crick gave his Nobel lecture almost a decade later, although immersed in the great wave of research in molecular genetics that the discoveries had unleashed, he was still in awe of the significance of these findings.

"It is," he wrote, "one of the striking generalisations of biochemistry - one which, surprisingly, is seldom mentioned in textbooks - that the 20 amino acids and four bases are, with minor exceptions, the same throughout Nature. As far as I am aware, the presently accepted set of 20 amino acids was first drawn up by Watson and myself in the summer of 1953, in response to a letter from [George] Gamow."

These are not the words of an immodest man. Indeed, by this time, Watson had written that he had "never seen Crick in a modest mood". That first line of The Double Helix was widely publicised, as if it were the back-biting spirit of the book itself.

It was not. The book raised eyebrows by its frankness, but it gave a brilliant insight into the process of scientific discovery, and revealed how Crick and Watson interacted with the same kind of two-way precision as the double helix itself. The first line was completely justified by Crick's confident, but exacting, belief in his own scientific perception.

Events showed he had good reason for his confidence. He went on to postulate the characteristics of the genetic code in much greater detail, invoking, on the way, the term "codon" for the individual base-pair triplets that were soon accepted as the specific codes for particular amino acids, and are now written indelibly into the language of science.

With Sidney Brenner and others, he embarked on the demanding investigation of how long sequences of base pairs - providing the codes for amino acid sequences in individual proteins - are isolated from the huge mass of information in the nucleus, and then read, with very few errors, during their rapid transcription in the living cell.

At this time, working again with Watson, who had spent a couple of years at the California Institute of Technology (Caltech), Crick investigated the RNA (ribonucleic acid) of viruses, and together they proposed models of viral structure which carried molecular biology into a new realm.

Most of this work was carried out in Cambridge, under the great Max Perutz, first in the Medical Research Council (MRC) department in the old building of the Cavendish laboratory and, later, in the new MRC laboratory of molecular biology a mile or two down the road. There, with spells in California at the Salk Institute, La Jolla, at Harvard and elsewhere in America, Crick spent much of his working life until 1977.

Then, urged by a need to broaden his research into the structure and function of complex biological systems - such as that of the brain - he became a distinguished professor at the Salk Institute and, in parallel, professor of biology, chemistry and psychology at the University of California, San Diego. Working alongside such giants of molecular genetics as Leslie Orgel, he probed increasingly deeply, with his cool and characteristic precision and insight, into the way structure and function are integrated in living things.

Crick was awarded the Order of Merit in 1991, and was still hard at work two years later, although formally retired, when the great biology laboratories of the world held a season of celebrations to mark the 40th anniversary of the publication of the Watson-Crick hypothesis.

Rarely do those who start revolutions live to see the changes they have wrought. But in March 1993, at Cold Spring Harbor laboratory, on Long Island, where Watson had become director in 1969, the two men recalled their collaboration, and stood at centre stage of an international review of the huge scientific developments in biology they had initiated.

At this meeting, Crick spoke with sharp, dry humour of the informality and fun of life in postwar Cambridge, when much of the thinking was done in pubs. Molecular biology, he seemed to be saying, has become weighed down by its great size and gravitas. He also spelt out very clearly how the work of Linus Pauling - who discovered the alpha-helix structure in proteins, and insisted that this branch of biology was really physical chemistry - had laid the foundations on which he, Watson and Wilkins had built.

Crick was born in Northampton, and went from his local grammar school to Mill Hill school, north London. His older brother had opted to study medicine (and after the war emigrated to New Zealand as a GP), but Francis chose physics at University College London. After graduating in 1937, he started to work toward a PhD under Prof EN de C Andrade, one of the pioneers of research into high-stress failure in engineering materials.

However, the outbreak of the second world war disrupted his studies, and he was drafted into the Admiralty Research Establishment, where he worked mainly on countermeasures to acoustic and magnetic mines. By 1945, partly persuaded by the writing and work of JD Bernal, but also, like many other physicists, seeking a career in the life sciences rather than in engineering or physics, he determined to study biology.

He went to the Strangeways laboratory, Cambridge, in 1947 under a medical research council grant and, already revealing an extraordinary gift for biochemistry, joined the MRC unit at the Cavendish, becoming a research student for the second time in 1950. The triumphant work with Watson and Wilkins was a component of his PhD studies; he finally received his doctorate in 1954.

Back in 1947, Crick had known no biology and little biochemistry or crystallography, yet, over the next few years (with Cochran and Vand) he worked out the general theory of X-ray diffraction by a helix and, at the same time as Pauling and Corey in America, suggested that the patterns being seen in proteins were those of alpha helices coiled round each other.

His lifelong friendship with Watson, who was a generation younger and also a postgraduate student when working on the structure of DNA, arose naturally from the recognition by each of the brilliance of the other.

Crick was married twice: in 1940, to Ruth Doreen Dodd, with whom he had a son, Michael, who went into science. This marriage ended in divorce in 1947, partly as a result of Crick's decision to switch careers and become a student again. Two years later, he married Odile Speed, with whom he had two daughters, Gabrielle and Jacqueline. His wife and children survive him.